chore(github): add Buy Me a Coffee to FUNDING.yml

https://buymeacoffee.com/remarkablemark

Author: remarkablemark

.github/FUNDING.yml

@@ -9,5 +9,6 @@ community_bridge: # Replace with a single Community Bridge project-name e.g., cl
 liberapay: remarkablemark # Replace with a single Liberapay username
 issuehunt: # Replace with a single IssueHunt username
 otechie: # Replace with a single Otechie username
+buy_me_a_coffee: remarkablemark
 thanks_dev: u/gh/remarkablemark
 custom: ['https://b.remarkabl.org/teespring'] # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']